Screening and Characterization of Phosphate-Solubilizing Rhizobia Isolated from Hedysarum pallidum in the Northeast of Morocco

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Why is it important?

Due to high cost of chemical fertilizers and negative environmental effects, the use of rhizobia as plant growth-promoting rhizobacteria (PGPR) has shown potentials to be a promising technique to assure a sustainable agriculture. Our goal was to select rhizobia strains isolated from nodules of Hydesarum pallidum plants present in Touissit, northeast of Morocco, exhibiting different activities that can stimulate directly and/or indirectly plant growth. A total of 37 bacteria were isolated, of which 19 were capable of solubilizing tricalcium phosphate (TCP). Based on the diameter of solubilization halos (diameter ≥0.4 cm), 15 strains were selected and evaluated for more PGP activities in vitro for selected isolates. As a result, 11 bacteria were proved to be able to synthesize hydrogen cyanide (HCN). Amounts of indole acetic acid (IAA) produced by these bacteria ranged between 1.04 and 3.43 mg L⁻¹. Their ability to secrete siderophores was also evaluated; 80% of the strains were positive for these compounds’ production. We also looked for extracellular enzymes such as cellulase, amylase, protease, chitinase, and urease. The percentages of bacteria that were positive for the production of these hydrolytic enzymes were, respectively, 73.3%, 93.3%, 40%, 26.67%, and 33.3%. Eight of selected bacteria were checked for quantitative assay of TCP solubilization, and soluble P concentrations were between 2 and 137 mg/L, accompanied by a drop in media pH from 5.67 to 3.87. This study reveals the potential of some rhizobia to be used as efficient biofertilizers.